Wicking boxes and beds are for people who like to grow at least some healthy vegetables but are short of time, water, suitable space or money. With wicking boxes, they can grow healthy vegetables in weekends, on balconies, concrete surfaces, near trees and on heavy clay soils. They are very water-efficient.
Wicking refers to water moving sideways and upwards without any external support due to its molecular structure. For the science-minded, wicking happens because a molecule of water has a positive and a negative end. These ends attract each other, making water molecules stick together. The power that links the molecules is not very strong, but is sufficient to pull the water up to 30cm.
Good soil, cloth, and other materials contain countless small channels called capillaries. These very small and connected channels make it possible for water to move up and sideways. Without them, or if they are blocked, wicking cannot happen. To see this in action, hang a wet towel half in and half out of a bucket of water, and watch as water slowly drips onto the surface. Wicking in soil works similarly but at a slower rate.
In some soils, wicking can draw water upwards to 300cm. This allows for a reservoir of water inside beds or boxes, enabling bottom-up watering in addition to the traditional surface-down method.
What Are Wicking Beds and Boxes?
Wicking beds and boxes are the containers we use to grow plants in a way which maximises water efficiency and provides an environment for optimal growth. They are waterproof or lined with a waterproof liner and have an overflow to allow for excess water to drain out. At the bottom of the container is a pipe filled with water that, with the surrounding soil, forms a reservoir of water that will wick up and water the roots. There is an overflow at the top of the pipe to drain excess water from rain or over-watering.
Advantages
Wicking beds and boxes offer numerous benefits:
- Suitable for many more locations as they can be placed near trees, on heavy clay soils, concrete, balconies, or even tables.
- A built-in water reservoir provides plants with consistent moisture over longer periods, reducing the need for frequent shallow watering as the water is stored in the root zone. This encourages root development and, with proper nutrition, ensures healthy soil and plants. (See our guide to making your own healthy soil)
- Optimised water use as they are self-contained; no water percolates below the box and tree roots cannot invade the beds. Over-watering is prevented by the overflow.
- Less frequent watering makes it a convenient weekend task, especially for busy individuals.
Warnings
Since we introduced wicking beds online 20+ years ago, several incorrect designs have emerged. To avoid these pitfalls, refer to our article on common misconceptions and wrong designs.
One major issue is designs that use stones and cloth to separate soil from the 90 mm PVC pipe. This approach is flawed because:
- The cloth creates an airlock, preventing wicking (air does not wick).
- Stones replace essential soil biology, which is crucial for plant health.
- Water-holding capacity is reduced.
For a detailed explanation of why these designs are ineffective, see the real cost of using cloth and stones in wicking boxes and beds. Disappointingly, even the ABC has promoted these flawed designs.
